Much progress has been made recently in understanding the autosomal dominant polycystic kidney disease (ADPKD), which affects millions of people world-wild. The main disease phenotype is characterized by the persistent proliferation and de-differentiation of renal epithelial cells that eventually form fluid-filled cysts. Gradually, these cysts cause anatomical distortion and kidney failure. One of the disease-causing genes, PKD2, has a significant overall sequence and structure conservation to various known cation channels. Recent study indicates that expression of PKD2 or a related protein PKDL is sufficient to produce Ca2+-permeable non-selective cation channel activities. Another ADPKD disease gene, PKD1, is also a transmembrane protein that has been shown to interact with PKD2. PKD 1 may regulate PKD2 channel activity which initiates yet undefined intracellular signal transduction pathway that maintains proper epithelial cell polarity, secretion and other functions. This proposal applies newly developed tools of functional genomics to the study of PKD2 gene through its homologue in Drosophila, namely the DmPKD2 gene. We have cloned the DmPKD2 gene and it shows similarities of 48 percent and 59 percent to human PKD2 in two most conserved regions that contain the predicted transmembrane segments. The N- and C-termini of DmPKD2.are more divergent. We propose here to test the hypothesis that DmPKD2 functions as a channel as was shown for other vertebrate PKD2-related proteins. The properties and regulation of DmPKD2 will be quantified. We also propose to test the channel function of DmPKD2 in its native environment, namely living fly epithelial tissues. Specifically, we will genetically over-express or ablate the production of DmPKD2 in culture cells (in vitro) and fly tissues (in vivo). Single channel analyses will be performed on both the wild-type and mutant cells and tissues where DmPKD2 is normally expressed. The long-term goal of this research is to define the biochemical pathway by which the PKD2 family of channels operates to regulate cell and developmental processes.